As defined in the UMTS specifications, the UMTS Terrestrial Radio Access Network (or UTRAN), which is responsible for handling all radio related functionality and which comprises a plurality of base stations (also called NodeB or primary stations), is linked to the user terminals (also called user equipments or secondary stations or mobile stations). The structure of the state of the art UTRA (Evolved Universal Terrestrial Network or E-UTRA, also known as LTE for Long Term Evolution) is captured 3GPP TS36.300, which is available from http://www.3gpp.org, incorporated herein by reference.
Regarding the uplink channels, i.e. from the secondary stations to the base stations, the secondary stations are transmitting data only on respective transmission resources, to avoid collisions of signals. These transmission resources are defined mainly by a frequency, a modulation coding scheme (MCS) and a transmission time interval during which they are allowed to transmit by using those parameters.
This can be done dynamically by sending on a downlink control channel, namely the Layer 1/Layer 2 downlink control channel (or L1/L2 control channel), an indication signal for allocation of an uplink physical resource, for instance in response to an allocation request of the secondary station. The Transmission Time Interval TTI is indicated by the time of transmission of this indication from the primary station to the secondary station: the allocated TTI will start after a fixed period starting from the sending of the indication signal. In this case, the timing of the transmission will be a fixed time period offset from the reception and decoding of the L1/L2 downlink control information.
As currently specified in UMTS LTE, the message that allocates the uplink resource also includes an indication requesting that the User Equipment sends a report on the quality of the down link channel (CQI or Channel Quality Indicator).